Tool for producing camshafts by expanding

ABSTRACT

A tool for producing expanded camshafts. The tool includes at least one modular die made up of segments that are joined together and that are provided with opposing slides for centering and aligning the cams around the axis of the shafts.

The present invention relates to the production of camshafts, especiallyfor reciprocating-piston internal combustion engines. More particularly,it relates to a device for holding in orientation, around a tubularshaft, a flat cam of ovoid contour perforated by an orifice throughwhich the said shaft passes, in view of fixation of the cam on the shaftby expanding the said shaft, as well as to a die equipped with aplurality of these devices and to a machine for production of camshaftsprovided with at least one such die.

From U.S. Pat. Nos. 4,781,076 and 4,858,295, for example, there isalready known a process for production of such a camshaft by expanding,wherein the said cams are disposed along a tubular shaft passing throughthem, after which the said shaft is expanded radially with plasticdeformation by forcing an expander tool into the interior thereof inorder to fix the said cams on the said shaft. To ensure such fixations,the orifice of the said cams is provided with irregularities of contour,into the hollows of which the peripheral material of the radiallyexpanded shaft penetrates.

The object of the present invention is to provide an advantageous toolfor application of such a process.

To this end, the invention relates very particularly to a device forholding in orientation, around a reference axis, a flat cam with ovoidperipheral contour perforated by an orifice through which there can bepassed a tubular shaft whose axis then coincides with the said referenceaxis, in view of fixation of the said cam on the said shaft by expandingthis shaft, this device being noteworthy in that it is provided with:

a body provided with a transverse passage for the said shaft and with aconduit for introduction of the said cam, the said introduction conduitopening at one end into the said transverse passage and at the other endat the periphery of the said body;

means for holding the said cam in its introduction conduit in a waitingposition in which its orifice is at least approximately coaxial with thesaid transverse passage;

two first sliding blocks, spaced apart and parallel, interlockinglymounted to move translationally in the said body in a manner that is atleast substantially orthogonal to the said transverse passage for thesaid shaft, the said first sliding blocks being elastically spread apartfrom the said transverse passage by first elastic means, with theirexternal ends projecting outside the said body on one side thereof andtheir internal ends disposed facing a part of the ovoid contour of thesaid cam when this is in the said waiting position;

two second sliding blocks, spaced apart and parallel, in mirror-imagerelationship to the said first sliding blocks and interlockingly mountedto move translationally in the said body, in a manner that is at leastsubstantially orthogonal to the said transverse passage for the saidshaft, the said second sliding blocks being elastically spread apartfrom the said transverse passage by second elastic means, with theirexternal ends projecting outside the said body on the other sidethereof, and their internal ends disposed facing another part of theovoid contour of the said cam when this is in the said waiting position;and

a mechanical linkage connecting the said first and second sliding blockssuch that, when the said first sliding blocks are pressed against theaction of the said first elastic means to displace the internal ends ofthe said first sliding blocks toward the said part of the ovoid contourof the said cam until contact is made therewith, the said second slidingblocks are pressed by the said mechanical linkage against the action ofthe said second elastic means to displace the internal ends of the saidsecond sliding blocks toward the said other part of the ovoid contour ofthe said cam until contact is made therewith.

Thus, in the device of the invention, each cam, starting from itswaiting position, is pressed in opposing directions by the said firstand second sliding blocks, which permits it to be displaced and to turnaround its axis so that on the one hand it eliminates the error of itsangular position due to the imprecision of introduction into the saidconduit by, for example, a robot, and on the other hand it compensatesfor the errors of precision in production of the said cam. It istherefore easily understood that the said cam is then centered andoriented precisely, regardless of the precision of its production and ofhow it is oriented relative to the introduction conduit.

Consequently, for a given cam contour and a given angular orientation ofthe cam, the relative lengths of the said first and second slidingblocks are themselves determined. To be able to adjust these relativelengths and therefore the centering and orientation of each cam, it isadvantageous for the said first and second sliding blocks to beadjustable in length. For this purpose they can be provided with aportion of fixed length and a portion of adjustable length comprised,for example, by a set of interchangeable shims of different lengths,with which the angular position of the cam can be adjusted. In addition,to improve the centering and orientation of the cam still further, it isadvantageous for the spacing between the said first sliding blocks andthe spacing between the said second sliding blocks to be determined as afunction of the contour of the cam and of the angular orientationthereof around the said shaft. These spacings are chosen so as to ensurethe largest possible lever arm on each sliding block, in order tofacilitate orientation while ensuring firm engagement of the said cam bythe said first and second sliding blocks in the said waiting position.

In order to facilitate the contact between the contour of the cam on theone hand and the internal ends of the said first and second slidingblocks on the other hand, these sliding blocks are provided with rollingmembers such as wheels that can roll over the said ovoid peripheralcontour.

Advantageously the said means for holding the said cam in waitingposition in its introduction conduit comprise a pressing pad pressedelastically toward a position-reference plate interlocked with the saiddevice, the said pressing pad being spread apart elastically from thisreference plate during introduction of the said cam flatly between thesaid pressing pad and the said reference plate. It is seen that the saidcam is in this way held by friction while being pressed between the saidpressing pad and the said reference plate, and the position of the camalong the said tubular shaft is easily adjustable by disposing thicknessshims in front of or behind the said reference plate. Preferably thesaid means for holding the cam are provided with a stop system againstwhich the said pressing pad is pressed elastically when no cam is inwaiting position, this stop system imposing, between the said pressingpad and the said reference plate, a minimum spacing smaller than thethickness of the said cam. In this case in particular, the said pressingpad can be provided with a chamfer on which the said cam, during itsdisplacement toward its waiting position in the said introductionconduit, exerts a pressure that causes the said pressing pad to bespread apart elastically relative to the said reference plate.

In a particularly advantageous embodiment of the device according to thepresent invention, the said holding means form a mechanical unitinserted and fixed in the said introduction circuit. Thus there can beprovided a plurality of different units, each specifically adapted to aparticular cam and interchangeable with the other units. Thus the saiddevice can be used for cams of different dimensions and shapes.

To ensure that it can be easily assembled in compact manner with othersimilar devices, the body of the said device according to the presentinvention advantageously has the form of a thick plate with parallelfaces. For purposes of greater compactness of an assembly of a pluralityof such devices, the slideways for the said first and second slidingblocks can be machined in a first of the said parallel faces of the saidplate, while the said introduction conduit is machined only partly inthis same first face, the second face of the said plate being machinedto form partly the introduction conduit of another plate, whose firstface can be applied against the said second face of the said plate.

Thus the present invention also relates to a die for production, byexpanding, of a tubular camshaft, especially for an internal combustionengine, the said cams being distributed along the said shaft withspecific orientations, the said die being provided with as many devicessimilar to that described as the said shaft has cams, the said devicesbeing assembled one after another in such a way that their transversepassages are aligned to form a channel for the said tubular shaft and insuch a way that their cam-introduction conduits are disposedrespectively at the position of a cam along the said shaft. In order toensure that such a die constituted by a succession of such deviceshaving a body in the form of a thick plate corresponds correctly to thepositions to be occupied by the said cams along the said shaft, it ispossible:

either to determine the thickness of the thick plate constituting thebody of each device as a function of the said positions;

or to produce all of the said devices with thick plates of identicalthickness and to provide thickness shims designed to be disposed betweenthe said devices.

Such a die can be mounted alone or with at least one identical die on amachine for the production of camshafts by expanding provided with asingle actuating member which commonly presses all of the said firstsliding blocks of the said die, the actuating member being mounted onthe said machine independently of the said die. Thus the control memberof the die is interlocked with the machine and not with the die, suchthat the die can be easily mounted and demounted on the machine, inorder, for example, to be replaced by another. It will be noted thatsuch mounting and demounting operations are facilitated by the fact thatthe die, constituted by a plate assembly, is compact. It is thereforeeasy to maneuver and can be automatically mounted and demounted on themachine.

To improve the compactness and ease of mounting and demounting of thedie even more, it is additionally provided that the stop designed toblock one end of the tubular shaft during expansion thereof is alsomounted on the said machine—and not on the die—independently of the saiddie, facing the said channel for the said tubular shaft.

Preferably the machine according to the present invention is equippedwith at least two such dies, each able to move from at least onecam-loading station to at least one expanding station then, afterdischarge of the expanded camshaft, from the said expanding station tothe said loading station.

It is therefore seen that, by virtue of the present invention, theexpanding machine has numerous advantages:

because it uses cam centering and orienting devices independent from oneanother and specific to each cam, it has great modularity;

since engagement of each cam by the sliding blocks is symmetric, theprecision of centering and orientation of each cam is high regardless ofthe precision of introduction and production of the said cams;

compactness is ensured by the constitution of the die by devices in theform of plates applied one against the other and assembled together;

interchangeability of the die is easy, since it is compact and does notcarry either the expander stop or the sliding-block control member;

adjustments of axial and angular position of the cams can be achievedeasily by shims as described hereinabove;

flexibility of the die is high, because it can be used for expandingcamshafts of different types using a majority of standard elements and aminimum of elements specific to a particular type of camshaft.

It will be clearly understood how the invention can be achieved byconsulting the figures of the attached drawing. On these figures, likereferences denote like elements.

FIG. 1 is an overhead view of an expander die according to the presentinvention, designed for production of a tubular camshaft.

FIGS. 2 and 3 are side views of the expander die of FIG. 1 along arrowsII and III respectively of the latter figure.

FIG. 4 shows in an overhead view two segments of the die of FIGS. 1 to3, the thickest of these segments being provided with a cam-holding unitand having its sliding blocks in spread-apart position, while the leastthick segment is illustrated without cam-holding units and with itssliding blocks in proximate position.

FIG. 5 is a schematic elevation view of the front of a segment of thedie of FIGS. 1 to 3, illustrated with its cam-holding unit removed fromthe introduction conduit of the said segment.

FIGS. 6 and 7 schematically show, in section along lines VI-VI andVII-VII respectively of FIG. 5, the assembly of a thicker segment and ofa less thick segment, the said segments being illustrated in FIG. 7 withtheir cam-holding units loaded respectively with such a cam.

FIGS. 8 and 9 show respectively in front view and in partly cutawayoverhead view a cam-holding unit for a segment of the expander dieaccording to the present invention.

FIG. 10 illustrates in front view a segment of the expander die providedwith its. cam-holding unit in introduction position of such a cam.

FIG. 11 is an overhead view of the cam-holding unit of the segment ofFIG. 10 just after introduction of such a cam between its pressing padand its reference plate.

FIGS. 12, 13 and 14 illustrate in schematic front views the centeringand angular orientation of the cam of FIG. 11 for three different valuesrespectively of the said angular orientation.

FIG. 15 is an overhead view of the cam-holding unit of the segment ofFIG. 10 after centering and angular orientation of the cam of FIG. 11,in the case of FIG. 14.

FIG. 16 is a schematic plan view of an expanding machine provided withtwo dies of FIGS. 1 to 3.

Expander die 1 illustrated in FIGS. 1 to 3 is intended for production ofa camshaft for an internal combustion engine, constituted from a tubularshaft 2 and a plurality of cams 3 distributed along tubular shaft 2. Asis evident from FIGS. 10 and 16, each cam 3 is flat and has an ovoidperipheral contour 4. In addition, it is perforated by a cylindricalorifice 5 provided with surface irregularities 6. In FIG. 1, die 1 isillustrated in a position for which all cams 3 are held with precisecentering and correct specific orientations and are traversed by tubularshaft 2. In this position, tubular shaft 2 is ready to be expanded toensure that its external cylindrical wall, expanded plastically by anexpander, is forced to fill orifices 5 and irregularities 6, in order tointerlock all said cams 3 with the said tubular shaft 2.

In the particular example of the camshaft illustrated in FIGS. 1 and 16,the cams 3 have been distributed in pairs, the axial distance betweenthe two cams of a pair being smaller than the axial distance between twoadjacent pairs.

Die 1 is provided with a base platen 7 provided with centering and/orfixation means 8. On base platen 7 there are mounted a plurality ofsegments 9, which are attached to one another. Segments 9 areinterlocked with platen 7 by, for example, keys 10 (see FIG. 5), and areassembled together by tie rods 11 provided with end nuts 12. Theassembly of segments 9 is closed at its ends by covers 13 and 14, ofwhich one (13) can be a simple end plate, whereas the other (14) has astructure similar to that of segments 9 and hereinafter is considered asa segment 9. Covers 13 and 14 are also provided with centering and/orfixation means 15.

Each segment 9, which is a device for holding a cam 3 in orientationaround a reference axis 16—the axis of the said cam 3 then coincidingwith the said axis 16—is provided with a body 17 which has the form of athick plate with parallel faces 18 and 19. In die 1, segments 9 areassembled in such a way that face 18 of one is applied against face 19of another. As is evident from FIGS. 1 to 4, 6 and 7, certain segments 9have a smaller thickness, in order to correspond to the axial distancebetween the two cams of a pair, while other segments 9 have a greaterthickness, in order to correspond to the axial distance between twoadjacent pairs of cams. More generally, the thickness of a segment 9 isdetermined by the position that cam 3 of the adjacent segment in die 1must occupy along tubular axis 2.

In body 17 of each segment 9 there is made a transverse passage 20centered on reference axis 16 and a radial conduit 21 for introductionof a cam 3. Introduction conduit 21 opens at one end into transversepassage 20 and at the other end at the upper periphery of body 17.

In die 1 there are provided as many segments 9—cover 14 of identicalstructure being counted as one segment 9—as there are cams 3 to bemounted on tubular axis 2, and the said segments are assembled one afteranother in such a way that their transverse passages 20 are aligned toform a channel 22 of axis 16, in order to receive the said tubular axis2, and in such a way that their introduction conduits 21 arerespectively disposed in correspondence with the position of a cam 3along the said shaft.

In order to reduce the longitudinal space requirement of the die, eachintroduction conduit 21 is constituted on the one hand by an undercut21A made in face 18 of the segment 9 in question and on the other handby an undercut 21B made in face 19 of the adjacent segment 9 beingapplied against the said face 18.

In each introduction conduit 21 there are provided means 23 for holdinga cam 3 in the said conduit in a waiting position in which itstransverse orifice 5 is at least approximately coaxial with thecorresponding transverse passage 20, or in other words with referenceaxis 16. Each means 23 of a segment 9 (see FIGS. 7, 8 and 9) is providedwith a pressing pad 24, cut out at 25 in the extension of transversepassage 20 and seated in undercut 21B of the adjacent segment 9, as wellas a reference plate 26, also cut out at 27 in the extension oftransverse passage 20 and seated in undercut 21A of the correspondingsegment 9, to which it is fixed. Pressing pad 24 is pressed elasticallytoward the associated reference plate 26 by springs 28, which flattensit against stops 29 when no cam 3 is in waiting position in holdingmeans 23. Stops 29 impose between pressing pad 24 and reference plate 26a minimum spacing e, which is smaller than the thickness E of a cam 3.It is therefore easily understood that, when a cam 3 is introducedflatly between the said pressing pad 24 and the said reference plate 26,the said pressing pad 24 is elastically spread apart from stops 29 andfrom the said reference plate 26 against the action of springs 28, andthat the said cam is held by pressure between the pressing pad and thereference plate.

To facilitate the introduction of a cam 3 between pressing pad 24 andreference plate 26, the said pressing pad 24 is provided on its rimfacing the inlet side of conduit 21 with a chamfer 30, on which the saidcam 3, during the said introduction, exerts a pressure that by wedgeeffect causes the said pressing pad 24 to be spread apart elasticallyfrom reference plate 26.

As illustrated by FIGS. 5, 8 and 9, the pressing pad 24, reference plate26, springs 28 and stops 29 together form a unit 23 that can beintroduced and fixed in an introduction conduit 21.

In addition, as is particularly evident in FIGS. 5 and 6, straightslideways 31 are machined in face 18 of segments 9 and of cover 14 for:

two first straight sliding blocks 32, spaced apart and parallel,disposed on one side of transverse passage 20 and mounted in thecorresponding slideways 31 in such a way that they can slidetranslationally relative to body 17 in a direction substantiallyorthogonal to the said transverse passage 20. First sliding blocks 32are elastically spread apart from transverse passage 20 by a spring 33braced against the said body 17. The internal ends of the two slidingblocks 32, directed toward transverse passage 20, are equipped withroller wheels 34. The external ends of the two sliding blocks 32 projectoutside body 17 and are translationally interlocked with one another bya push bar 35 carrying a spring cushioning element 36; and

two second straight sliding blocks 37, spaced apart and mutuallyparallel in the same way as first sliding blocks 32, disposed inmirror-image relationship to the latter on the other side of transversepassage 20 and mounted in their corresponding slideways 31 in such a waythat they can slide translationally relative to the said body 17 in adirection substantially orthogonal to transverse passage 20. Secondsliding blocks 37 are elastically spread apart from transverse passage20 by a spring 38 braced against the said body 17. The internal ends ofthe two sliding blocks 37, directed toward transverse passage 20, areequipped with roller wheels 34. The external ends of the two slidingblocks 37 project outside body 17 and are translationally interlockedwith one another by a cam bar 39.

In addition, a mechanical linkage 40 connects the two first slidingblocks 32 with the two second sliding blocks 37. This mechanical linkageis provided with a push rod 41, connected at one of its ends to the saidpush bar 35 and at its opposite end to one of the ends of a bell-cranklever 42, mounted to pivot around an intermediate fixed pin 43 carriedby body 17. The other end of bell-crank lever 42 is braced against cambar 39. Thus, when an actuating member 44 presses push bar 35 viacushioning element 36, first sliding blocks 32 are pressed against theelastic action of spring 33 in such a way that their wheels 34 providedat their internal ends are displaced toward introduction conduit 21. Thesame effect takes place symmetrically for wheels 34 provided at theinternal ends of second sliding blocks 37, by virtue of the action thatpush rod 41 and bell-crank lever 42 exert via cam bar 39 on spring 38.Conversely, when the action of actuating member 44 on bar 35 ceases,springs 33 and 38 elastically push the said first and second slidingblocks back and spread them apart from introduction conduit 21. Stops(not illustrated) are provided to limit the return travel of the saidsliding blocks under the relaxation action of springs 33 and 38.

The length of each of the sliding blocks 32 and 37 can be adjusted by,for example, interchangeable shims 45 disposed respectively between pushbar 35 and the external ends of first sliding blocks 32 and between cambar 39 and the external ends of second sliding blocks 37. Shims 45 canbe interlocked with the external ends of the said sliding blocks 32 and37 and/or of bars 35 and 39 by joints of the mortise and tenon type, forexample (not illustrated).

In addition, in segments 9, the spacing d1 between the first slidingblocks 32 and/or the spacing d2 between the second sliding blocks can bedifferent from one segment 9 to another (FIG. 10).

Thus, as illustrated by FIGS. 12 to 14, there is associated, with a cam3 that must occupy a given angular position around reference axis 16, asegment 9 whose spacings d1 and/or d2 are most suitable for engagementwith the said cam. Then, by means of interchangeable shims 45, thelength of the said sliding blocks 32 and 37 is adjusted to the valuethat is optimal for holding cam 3 in this given angular position. Ineach case, the choice of a segment 9 with its particular spacing d1 andd2 is determined by calculation, while adjustment of the length of eachof sliding blocks 32 and 37 with specific shims 45 is achieved bymeasurements using standard cams, identical to the said cams 3 anddisposed in the angular positions desired for the said cams 3. FIGS. 12,13 and 14 illustrate three examples of adjustments with differentspacings d1 and/or d2 and different shims 45, these three examplescorresponding respectively, for cams 3, to a vertical position pointingup, to a horizontal position pointing left and to a 45° positionpointing up and right.

It will be further noted that the axial position of each cam 3 alongtubular shaft 2 can be adjusted—also by tests—by a shim of thickness 46(see FIG. 7) disposed, for example, between reference plate 27 of means23 and body 17 of the corresponding segment 9.

Thus, once the different choices of d1, d2 and the different adjustmentshave been made in die 1 by means of shims 45 and 46, cams 3 can now beloaded.

Each cam 3, which is carried, for example, by the arm of a robot (notillustrated), is brought above the corresponding introduction conduit 21in such a way that it partly overhangs chamfer 30 of pressing pad 24 inquestion. The robot lowers the said cam 3 which, while being bracedagainst the said chamfer 30, pushes pressing pad 24 back against theaction of springs 28 and spreads it apart from reference plate 26. Cam 3can therefore be inserted flatly between the said pressing pad 24 andreference plate 26, which press it elastically between them. The robotthen brings the said cam 3 into a waiting position 3A, in which itsorifice 5 is at least approximately coaxial with reference axis 16. Sucha waiting position 3A, in which the said cam 3 is held by friction, isillustrated in FIGS. 10 and 11.

After all cams 3 have been loaded into die 1—each then being disposed inits waiting position—actuating member 44, which is common to allsegments 9 of this die, acts on all of the push bars 35, in such a waythat wheels 34 of sliding blocks 32 and wheels 34 of sliding blocks 37are displaced toward the portion facing the ovoid contour 4 of cams 3,until contact with the said contour is made. Wheels 34 of sliding blocks32 and 37 therefore exert on cams 3 forces and/or torques that adjustthe centering and angular orientation of the said cams 3, incorrespondence with the chosen spacings d1, d2 and the thickness ofinterposed shims 45. In this way, all cams 3 are then centered onreference axis 16, with the position and angular orientation desired forthe camshaft (see FIGS. 12 to 15).

After introduction of the said tubular shaft 2 through all of the saidcams held in die 1—either before or after these cams have been blockedin position—the said tubular shaft 2 can be expanded—after the said cams3 have been blocked in position—in order to interlock the said cams 3and the said shaft 2.

To discharge camshaft 2, 3 produced in this way, actuating member 44 iscommanded to release the pressure that it is exerting on push bars 35.Springs 33 and 38 then push sliding blocks 32 and 37 back in such a waythat camshaft 2, 3 can be removed from die 1.

FIG. 16 schematically shows a machine 47 for production of expandedcamshafts according to the invention by using two dies 1 of theinvention, denoted respectively by 1.1 and 1.2. These dies 1.1 and 1.2are carried by a movable support 48, for example of rotary type, whichis capable of moving each die from a first working station P1 to asecond working station P2, then from this back to the first workingstation P1, one of the dies 1.1 (or 1.2) being disposed at the firstworking station P1 while the other 1.2 (or 1.1) is disposed at thesecond working station P2 and vice versa.

At the first working station P1, each die is loaded with cams 3 in theway described hereinabove. At the second working station P2 there isprovided the said common actuating member 44, which ensures correctcentering and angular orientation of cams 3. At this station it istherefore possible to introduce tubular shaft 2 into cams 3 of the saiddies, then to expand the said shaft 2 by means of an expander 49, thesaid shaft then being against a stop 50—for example of retractabletype—provided at the second station P2.

What is claimed is:
 1. A device for holding in orientation, around areference axis, a flat cam with an ovoid peripheral contour perforatedby an orifice through which a tubular shaft can be passed, an axis ofthe tubular shaft coinciding with the reference axis, in view offixation of the cam on the shaft by expanding the shaft, comprising: abody provided with a transverse passage for the shaft and with anintroduction conduit for introduction of the cam, the introductionconduit opening at a first end into the transverse passage and at asecond end at a periphery of the body; means for holding the cam in theintroduction conduit in a waiting position in which the orifice is atleast approximately coaxial with the transverse passage; two firstsliding blocks, spaced apart and parallel, interlockingly mounted tomove translationally in the body in a manner that is at leastsubstantially orthogonal to the transverse passage for the shaft, thefirst sliding blocks being elastically spread apart from the transversepassage by first elastic means, with their external ends projectingoutside the body on a first side of the body and their internal endsdisposed facing a part of the ovoid peripheral contour of the cam whenthe cam is in a waiting position; two second sliding blocks, spacedapart and parallel, in mirror-image relationship to the first slidingblocks and interlockingly mounted to move translationally in the body,in a manner that is at least substantially orthogonal to the transversepassage for the shaft, the second sliding blocks being elasticallyspread apart from the transverse passage by second elastic means, withtheir external ends projecting outside the body on a second side of thebody, and their internal ends disposed facing another part of the ovoidperipheral contour of the cam when the cam is in the waiting position;and a mechanical linkage connecting the first and second sliding blockssuch that, when the first sliding blocks are pressed against action ofthe first elastic means to displace the internal ends of the firstsliding blocks toward a part of the ovoid peripheral contour of the camuntil contact is made therewith, the second sliding blocks are pressedby the mechanical linkage against action of the second elastic means todisplace the internal ends of the second sliding blocks toward a secondpart of the ovoid peripheral contour of the cam until contact is madetherewith.
 2. A device according to claim 1, wherein lengths of each ofthe first and second sliding blocks are determined by the ovoidperipheral contour of the cam and by an angular orientation of the camaround the shaft.
 3. A device according to claim 2, wherein the firstand second sliding blocks are adjustable in length.
 4. A deviceaccording to claim 1, wherein the spacing between the first slidingblocks and the spacing between the second sliding blocks are determinedby the ovoid peripheral contour of the cam and by an angular orientationof the cam around the shaft.
 5. A device according to claim 1, whereinthe internal ends of the first and second sliding blocks are providedwith rolling members for contact with the ovoid peripheral contour ofthe cam.
 6. A device according to claim 1, wherein the means for holdingthe cam in the waiting position in the introduction conduit comprises apressing pad pressed elastically toward a reference plate interlockedwith the device, the pressing pad being spread apart elastically fromthe reference plate during introduction of the cam flatly between thepressing pad and the reference plate.
 7. A device according to claim 6,wherein the means for holding the cam further comprises a stop systemagainst which the pressing pad is pressed elastically when no cam is inthe waiting position, the stop system imposing, between the pressing padand the reference plate, a minimum spacing smaller than a thickness ofthe cam.
 8. A device according to claim 6, wherein the pressing padincludes a chamfer on which the cam, during displacement toward thewaiting position in the introduction conduit, exerts a pressure thatcauses the pressing pad to be spread apart elastically relative to thereference plate.
 9. A device according to claim 6, wherein the means forholding the cam forms a mechanical unit inserted and fixed in theintroduction conduit.
 10. A device according to claim 1, wherein thebody has a form of a thick plate with parallel first and second faces.11. A device according to claim 10, wherein slideways for the first andsecond sliding blocks are machined in the first parallel face of theplate, while the introduction conduit is machined only partly in thefirst face, the second face of the plate being machined to form partlythe introduction conduit of another plate, whose first face isconfigured to be applied against the second face of the plate.
 12. A diefor production, by expanding, of a tubular camshaft, cams beingdistributed along the shaft with specific orientations, provided with asmany devices according to claim 1 as the shaft has cams, the devicesbeing assembled one after another such that their transverse passagesare aligned to form a channel for the tubular shaft and such that theircam introduction conduits are disposed respectively at a position of acam along the shaft.
 13. A die according to claim 12, wherein for eachdevice each respective body has a form of a thick plate with parallelfirst and second faces, and wherein a thickness of each thick plateconstituting each body of each device is determined by positions to beoccupied by the cams along the shaft.
 14. A die according to claim 13,wherein the bodies of all of the devices have identical thickness, andwherein thickness shims configured to be interposed between the devicesare provided to ensure correct correspondence with positions to beoccupied by the cams along the shaft.
 15. A machine for production, byexpanding, of a tubular camshaft, in which cams are distributed along ashaft with specific orientations, provided with at least one dieaccording to claim 12 and with a single actuating member for commonlypressing all of the first sliding blocks of the die, the actuatingmember being mounted on the machine independently of the die.
 16. Amachine according to claim 15, provided with a stop for blocking, duringan expanding operation, one end of the tubular shaft passing through thecams, the stop being mounted on the machine, independently of the die,facing the channel for the tubular shaft.
 17. A machine according toclaim 15, equipped with at least two dies, each able to move from atleast one cam-loading station to at least one expanding station then,after discharge of the expanded camshaft, from the expanding station tothe loading station.